The invention relates to a centrifugal fan and, in particular, to a centrifugal fun with a fan frame that can enhance fan performance substantially. Electronic devices generally produce heat during operation, and thus the demand for effective heat-dissipation devices has increased. Therefore, a heat-dissipating device or a centrifugal fan must offer optimal perforniance to dissipate the excess heat. As shown in FIG. 1, a conventional centrifugal fan 1 includes a fan frame F and an impeller I. FIG. 1 is a perspective view of a combination of the fan frame F and the impeller I. FIG. 2 is a perspective view of the fan frame F. The fan frame F includes a frame F′ and a sleeve S. The impeller I is disposed F′ of the fan frame F comprises a curved wall W, a bottom portion B, and a first guide portion G.
Higher air pressure increases the amount of airflow and speed, and vice versa. The fan frame structure F is one of the main factors affecting the air pressure level. In the conventional design, when the fan operates, airflow is produced and flows along the curved wall between the guide portion G and the impeller I. However, since the guide portion G has a flat elevation as shown in FIG. 3, the airflow surrounding the impeller I is disturbed, thereby producing cyclonic airflow and reducing air pressure. Thus, the total performance of the fan is reduced accordingly. Specifically, turbulent flow is produced at the inlet, and a certain level of flow resistance is generated. Thus, the guide portion & with a flat elevation is unable to efficiently guide the airflow, but adversely reduces the heat dissipation performance of the fan.
Since the above method does not satisfy performance demands, there is still a need for a fan structure offering enhanced performance without increasing the overall size of the fan that can minimize the airflow disturbance produced along a flow path between the fan frame and the impeller to maximize the airflow and air pressure.